President Barack Obama went behind bars on Thursday — extending his campaign for reform in the criminal justice system — becoming the first sitting president to see the inside a federal prison first hand.

The president visited the sprawling El Reno Federal Correctional Institution in Oklahoma, a complex which includes sections of buildings separated by large green yards and barbed wire fences. While there, he met with six inmates in prison for drug offenses.

"Every single one of them emphasized the fact that they had done something wrong, they are prepared to take responsibility for it, but they also urged us to think about how society could've reached them earlier on in life to keep them out of trouble," the president said.

The president has highlighted inequities in the criminal justice system all week.

On Monday, he commuted the federal prison sentences of 46 nonviolent drug offenders, 14 of whom were serving life terms. And on Tuesday, in a speech to the NAACP in Philadelphia, Obama argued for shortening or eliminating mandatory minimum sentences for those same offenders, and against solitary confinement.

"We have to consider whether this is the smartest way for us to both control crime and rehabilitate individuals," the president said Thursday. "We have to reconsider whether 20 year, 30 year, life sentences for nonviolent crimes is the best way for us to solve these problems."

We could eliminate tuition at every public college and university in America with the $80 billion we spend each year on incarcerations.

There are an estimated 1,574,700 people in state and federal prisons, according to 2013 figures from the Bureau of Justice Statistics.

Black men had higher imprisonment rates across all age groups. Similarly, black women's imprisonment rates were twice those of white women.

There are more than 200,000 people incarcerated at federal prisons like the one the president visited, according to figures from the Federal Bureau of Prisons. Roughly 48% were incarcerated on drug related offenses and nearly 50% of the federal prison population is between the ages of 26 and 40.

The president described the prisoners he met Thursday as "young people who made mistakes that aren't that different from the mistakes I made and the mistakes that a lot of you guys made."

And, as he has in the past in talking about the impact of socioeconomic inequity, he stressed that many of the types of inmates he met with didn't have the "the kind of support structures, the second chances, the resources that would allow them to survive those mistakes."

Criminal justice reform and, in particular disproportionate sentencing on minorities, is an area of common ground between the president and some congressional Republicans. Kentucky senator and Republican presidential candidate Rand Paul, for example, had pushed for changes to reduce mandatory minimum sentences for drug crimes and restore the rights of felons to vote.

Judiciary Committee Chairman Chuck Grassley, R-Iowa, has also been working on bipartisan legislation aimed at reducing mandatory minimum sentencing in some situations.

New Jersey Sen. Corey Booker, who has worked with Paul on criminal justice reform legislation, told MSNBC he welcomes the president's highlighting of a "broken system."

"There are collateral consequences," Booker said of high incarceration rates and the impact on former inmates. "They can't get jobs, loans, Pell Grants...all they want when they come out of prison is to work and we put a barrier on their lives."